Maternal homozygosity for the common MTHFR mutation as a potential risk factor for offspring with limb defects

Folic acid supplementation and risk for congenital limb reduction defects in China

BACKGROUND

Folic acid (FA) supplementation prevents neural tube defects, but there are mixed results for its ability to prevent limb reduction defects. We examined whether a preventive effect of FA supplementation exists for congenital limb reduction defects in a large population in China.

METHODS

Data from a large population-based cohort study in China were used to evaluate the effects of FA supplementation on birth defects. All births at 20 complete gestational weeks, including live births, stillbirths and pregnancy terminations, and all structural congenital anomalies, regardless of gestational week, were recorded. A total of 247 831 singleton live births delivered at gestational ages of 20-42 weeks to women from northern and southern China with full information on FA intake were included. Limb reduction defects were classified by subtype and maternal FA supplementation.

RESULTS

The prevalence of limb reduction defects was 2.7 per 10 000 births among women who took FA compared with 9.7 per 10 000 births among those who did not take FA in northern China; the prevalence was 4.5 and 3.8 per 10 000 births, respectively, in southern China. In both unadjusted and adjusted analyses, the estimated relative risk for upper limb reduction defects [odds ratio (OR) = 0.17, 95% confidence interval (CI): 0.04, 0.63] and total limb reduction defects (OR = 0.24, 95% CI: 0.08, 0.70) in northern China, but not for lower limb reduction defects ,was significantly decreased in association with FA supplementation in northern China. There was no association between FA supplementation and either an increased or decreased risk for limb reduction defects in southern China.

CONCLUSIONS

FA supplementation successfully reduces the prevalence of limb reduction defects in northern China, whose population has low folate concentrations.

Association between selected folate pathway polymorphisms and nonsyndromic limb reduction defects: a case-parental analysis

Inadequate folate status resulting from either genetic variation or nutritional deficiencies has been associated with an increased risk of congenital malformations including orofacial clefting, limb, cardiac and neural tube defects. Few epidemiological studies have examined the association between limb reduction defects (LRDs) and folate-related genetic polymorphisms other than MTHFR 677C→T. We conducted a case-parental analysis of 148 families who participated in the National Birth Defects Prevention Study to examine the association between nonsyndromic transverse and longitudinal LRDs with five single nucleotide polymorphisms (SNPs) in genes encoding enzymes in folate and methionine pathways. Log-linear Poisson regression, adapted for analysis of case-parental data assuming an additive genetic model, was used to estimate genetic relative risks and 95% confidence intervals for the association between LRDs and each SNP. Among women who did not take multivitamin supplements, the MTHFR 677T variant acts via the offspring's genome to increase the risk of LRDs. No association between LRDs and any fetal SNP was found among women who used multivitamin supplements. These results suggest the possibility that initiating folic acid supplementation prior to pregnancy may reduce the risk of having a LRD-affected pregnancy, especially in women whose offspring inherit one or two copies of the MTHFR 677T variant.

Maternal nutrient intake and risks for transverse and longitudinal limb deficiencies: data from the National Birth Defects Prevention Study, 1997-2003

BACKGROUND

The association between periconceptional intake of supplements containing folic acid with specific subtypes of limb deficiencies has been inconsistent. The objective was to investigate whether intake of nutrients involved in one-carbon metabolism (folate, vitamin B(6), vitamin B(12), riboflavin, choline, betaine, zinc, and methionine) through diet alone or in combination with a supplement containing folic acid influenced the risk for transverse limb deficiency (TLD) and longitudinal limb deficiency (LLD).

METHODS

We analyzed 1997-2003 data from the National Birth Defects Prevention Study and included 324 case infants with TLD, 158 case infants with LLD, and 4982 nonmalformed control infants. A food frequency questionnaire was used to estimate nutrient intakes. Use of supplements containing folic acid 1 month before through 2 months after conception was recorded.

RESULTS

Use of a supplement containing folic acid was not associated with LLD or TLD. For nonsupplement users, within (1) the lowest quartile of dietary folate intake or vitamin B(6) intake, adjusted odds ratios (aORs) for LLD were, respectively, 3.86 (95% confidence interval [CI]: 1.08-13.78) and 4.36 (95% CI: 0.93-20.48); and (2) the lowest quartile for riboflavin intake, the aOR for TLD was 2.94 (95% CI: 1.04-8.32). For supplement users within the lowest quartile of folate intake or riboflavin intake, the aORs for TLD were, respectively, 1.52 (95% CI: 0.91-2.54) and 1.54 (95% CI: 1.00-2.37).

CONCLUSIONS

TLD and LLD were not associated with supplement use, but TLD was associated with low intakes of riboflavin from diet.

Association of preterm birth with brain malformations

This study investigates the rate of preterm birth in babies with congenital brain defects. Autopsy case reports of congenital brain anomalies were obtained from the literature. The control cases were from a large registry, a published report from the Metropolitan Atlanta Congenital Defects Program. From 428 publications, 1168 cases were abstracted that had autopsy studies of congenital brain defects and information on the gestational age (GA) at birth. The control data from Atlanta included 7738 infants with significant birth defects of any kind and 264,392 infants without birth defects. In the autopsy cases with brain defects, the mean GA was 36.6 wk, whereas the Atlanta data showed a mean GA of 39.3 wk for infants with no defects and a significantly shorter gestation of 38.1 wk (p < 0.0001) for infants with defects. In the Atlanta data, the rate of preterm birth was 9.3% for those with no defects compared with 21.5% (p < 0.0001) for those with defects. In the autopsy cases with brain defects, the rate of preterm birth was even greater (33.1%, p < 0.0001). In conclusion, these data show an association of brain defects with preterm births.

Is multicenter collaborative research in clinical genetics dead and, if so, what killed it?

This study describes the course of a clinical trial designed to investigate the possible role of thrombophilic factors in limb reduction defects, which was abandoned after 1 year because lack of progress of the project through ethics review and the failure to make significant inroads in patient recruitment. Factors that are thought to have contributed to the failure are discussed, in the hope that others can avoid some of the pitfalls.

Methylenetetrahydrofolate reductase gene polymorphisms and their association with trisomy 21

OBJECTIVES

To verify whether the frequencies of 5,10-methylenotetrahydrofolate reductase (MTHFR) polymorphisms at positions 677 and 1298 are higher in women with children affected by trisomy 21 than in those with chromosomally normal offspring.

METHODS

A case-control study was carried out with 70 women whose children had trisomy 21 and 88 controls whose children were chromosomally normal. The frequencies of polymorphisms of points C677T and A1298C of MTHFR gene coding were studied in these two groups. Odds ratios (OR) for having a child affected by trisomy 21 were estimated for homozygosis, heterozygosis or the absence of the above-mentioned MTHFR polymorphisms. Logistic regression models were used to control for the effect of confounding variables on these odds ratios.

RESULTS

The frequency of joint heterozygotic polymorphism (677 and 1298) was significantly higher in women with children affected by trisomy 21 than in those with chromosomally normal offspring (OR: 5.7).

CONCLUSIONS

The presence of joint heterozygotic polymorphism in the codifying gene for MTHFR was a risk factor for having a child with trisomy 21.

Associations between maternal methylenetetrahydrofolate reductase polymorphisms and adverse outcomes of pregnancy: the Hordaland Homocysteine Study

PURPOSE

Methylenetetrahydrofolate reductase (MTHFR) is involved in the metabolism of folate and homocysteine; a polymorphism in the MTHFR gene (677C-->T) has been associated with adverse outcomes of pregnancy. We studied whether two polymorphisms in the MTHFR gene (677C-->T and 1298A-->C) are associated with pregnancy complications, adverse outcomes, and birth defects.

METHODS

MTHFR polymorphisms were determined in blood collected in 1992 and 1993 from 5883 women aged 40 to 42 years, and linked with 14,492 pregnancies in the same women recorded in the Medical Birth Registry of Norway from 1967 to 1996.

RESULTS

The 677TT genotype in mothers was associated with increased risk of placental abruption (odds ratio [OR] = 2.6; 95% confidence interval [CI]: 1.4 to 4.8) compared with the CC variant. The risk of intrauterine growth restriction increased with number of T alleles (P for trend = 0.04). Compared with the 1298AA variant, the CC variant was associated with a reduced risk of very low birth weight infants (OR = 0.4; 95% CI: 0.2 to 0.8). No significant associations were found between MTHFR polymorphisms and birth defects.

CONCLUSION

The maternal MTHFR 677C-->T polymorphism was a risk factor for placental abruption. The unexpected protective effect of the 1298A-->C polymorphism on very low birth weight needs further study.

High incidence of two methylenetetrahydrofolate reductase mutations (C677T and A1298C) in Hispanics

Mutations in the 5,10-methylenetetrahydrofolate reductase (MTHFR) and coagulation factors II and V genes have been found at high frequencies in European and American Caucasian populations and are associated with increased risk for thrombophilia, premature coronary artery disease, and a variety of adverse pregnancy outcomes. Hispanic populations in the United States exhibit high levels of some of these conditions, so we initiated a population-based study to determine the frequency of these mutations (MTHFR C677T and A1298C, Factor II G20210A and Factor V G1691A) in this group. We find comparable frequencies of the Factors II and V mutations, but a high incidence of the two MTHFR mutations in a diverse sample of American Hispanics compared to those reported in Caucasians. Prospective studies of Hispanic women with these mutations and pregnancy outcomes will establish if there is a causal relationship.

Poland anomaly--report of an unusual family

A family with classical Poland anomaly presenting in the son and a partially affected mother is reported. We hypothesize that Poland anomaly has a multifactorial basis involving vascular compromise in early development. Two possible predisposing factors are aberrant vascular formation and thrombophilia. The investigation of our family has not demonstrated an abnormality in coagulation, therefore, we surmise that an inherited structural variant of blood vessel formation is responsible.